Dirigent protein

This biocatalytic method is therefore quite promising for the synthesis of complex molecules. Very recently, it was reported 1121] that HRP catalyzes the oxidation of 2-naphthols to l,l -binaphthyl-2,2 -diols with moderate enantiomeric excess (ee 38-64%) (Eq. 5). However, in view of the analytical techniques used, these data have to be questioned [167]. As shown recently, atrop-selective biaryl coupling can only be achieved by means of dirigent protein as chiral auxiliary [122]. 

Fig. 12.4 Biosynthetic pathway for lignans with 9,9 -oxygen including yatein and fxsdophyUo-toxin. DP dirigent protein, PLR pinoresinol/laiiciresinol reductase, PrR pinoresinol reductase, and SIRD secoisolariciresinol dehydrogenase...

DIrIgent protein Free radical capture and stereoselective coupling... 

Fig. 12.6 Enantioselective formation of pinoresinol. Forsythia intermedia dirigent protein mediates selective formation of (-l-)-pinoresinol...

Davin LB, Wang H-B, Crowell AL et al (1997) Stereoselective bimolecular phenoxy radical coupling by an auxiliary (dirigent) protein without an active center. Science 275 362-366... 

The stereo-selective formation of certain lignans has been shown to be mediated by dirigent proteins. These proteins hold the monolignols in a specific orientation, but have no catalytic activity (Davin et al., 1997 see also Chapter 3). 

Figure 3-10. Dirigent-protein mediated formation of (+)-pinoresinol from two coniferyl alcohol radicals. The formation of the ring results from intramolecular cyclization.

Davin, L. B., and Lewis, N. G., 2000, Dirigent proteins and dirigent sites explain the mystery of specificity of radical precursor coupling in lignan and lignin biosynthesis, Plant Physiol. 123 453-461. 

Figure 4.8 Biosynthetic pathway from coniferyl alcohol to (—)-matairesinol. Enzymes and proteins Involved are (1) pinoresinol synthase (laccase + dirigent protein), (2) pinoresinol/lariciresinol synthase, (3) secoisolariciresinol dehydrogenase.

Halls, S.C. and Lewis, N.G. (2002) Secondary and quaternary structures of the (+)—pinoresinol forming dirigent protein. Biochemistry, 41, 9455-61. 

Kwon, M., Buriat, V., Davrn, L.B. and Lewis, N.G. (1999) Localization of dirigent protein involved in lignan biosynthesis implications for lignification at the tissue and subcellular level. Basic Life Sci., 66, 393-411. 

Lewis, N.G. and Davin, L.B. (2000) Phenolic coupling in planta Dirigent proteins, diri-gent sites and notions beyond randomness. Part 1. Polyphenols Actualites, 20,18-26. 

Ralph, S., Park, J.Y, Bohlmarm, J. and Mansfield, S.D. (2006) Dirigent proteins in conifer defense gene discovery, phytogeny, and differential wound- and insect-induced expression of a family of DIR and DlR-like genes in spruce (Picea spp.). Plant Mol Biol, 60,21 0. 

Carefully designed labeling experiments have conclusively established the biosynthetic origin of (-)-matairesinol in Forsythia spp. Cell-free enzyme preparations of F. suspensa stems catalyze the stereoselective coupling of two molecules of [8-14C]coniferyl alcohol to form (+)-pinoresinol in enantiomeric excess [24], This reaction likely involves the coupling of free radicals of coniferyl alcohol and is mediated by two enzymes an oxidase and a dirigent protein that controls the... 

Fig. (4). Proposed lignan biosynthetic pathway in Podophyllum (steps 1-3 have been characterized in Forsythia spp.). 1, Oxidase and dirigent protein create an 8-8 bond between two molecules of coniferyl alcohol 2, NADPH reductase catalyses two sequential reactions 3, NADP+ dehydrogenase. Dotted arrows indicate multiple uncharacterized steps.

In this context, the studies on the mutants and transgenic plants permitted to evidence dirigent proteins which are involved in the coupling of monolignols to form lignin polymer [54, 55] (Fig. 8.3). 

Fig. 8.3 The dirigent protein model for lignin formation proposed by Hatfield and Vermerris [54]...

The random biosynthesis process is imder review. Dirigent proteins, acting as templates, are proposed to assist the orientation of hgnin precursors to afford stereoselective phenoxy radical coupling (2,3). 

Figure 8.6 Podophyllotoxin biosynthetic pathway. DIR, dirigent protein PLR, pinoresinol-lariciresinol reductase SDH, sec-oisolariciresinol dehydrogenase PS, pluviatolide synthase OMT3, O-methyltransferase 3 CYPx, cytochromes P450 (CYP71CU1) OMT1, O-methyltransferase 1 and 2-ODD,...

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